Sintered compacts obtained by powder metallurgy are widely used for various kinds of parts, dies, molds and structural members because articles of complex shape can be easily obtained with minimum machining, high yield and high productivity.
However, the uses of these compacts are limited. The reason for this is that the ordinary sintered material always contains pores and therefor is not equal to the conventional wrought material in strength, corrosion resistance, wear resistance and surface precision.
Particularly, articles which must have a high degree of dimensional precision and a high degree of surface finish must be treated by infiltration, liquid sintering or hot isostatic pressing. In addition, they must be machined and finished just as well as wrought materials. In such cases, the merits of powder metallurgy are not sufficiently realized.
One of the ways to improve the surface properties of sintered materials is concerned with plating. Actually, to improve the surface properties of sintered material, attempts have been made to apply the electroplating process. But, in this process, troubles remain which result in less corrosion resistance because the electrolyte infiltrates into the pores of the sintered material and is enclosed therein. Additionally, it is very difficult to get a mirror-finished surface.